OSC Colloquium: Michel Digonnet

    Thursday, February 18, 2021 - 3:30pm - 5:00pm
    Virtual Via Zoom

    Open to campus and public.


    Public Video Unavailable, Internal Release only


    Speaker: Michel Digonnet

    Topic: Cooling Fiber Lasers with Anti-Stokes Fluorescence

    Zoom Link to Attend - https://arizona.zoom.us/j/94012959093

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    Few technologies have had the far-reaching global impact of rare-earth-doped fibers, especially in the context of fiber lasers, which are now critical to many scientific disciplines and industries ranging from communication systems to high-precision sensing and chip manufacturing. A persistent problem with fiber lasers, and lasers in general, is the generation of waste heat due to the fundamental quantum defect, which has strong deleterious effects on the laser power and frequency stability, coherence, and mode purity. This problem is managed with conventional refrigeration techniques such as water and thermoelectric coolers, which are cumbersome and also deteriorate the noise and frequency stability of the laser.

    Optical refrigeration (laser cooling) through the use of anti-Stokes fluorescence (ASF) provides a superior solution, compact and vibration free. The gain medium is pumped at a wavelength higher than its mean fluorescence wavelength, so that phonons are annihilated rather than generated. Since its first demonstration in 1995, a select few rare-earth-doped bulk materials have exhibited ASF cooling, and almost exclusively in a vacuum. With the exception of Yb-doped fluorozirconates, all these materials are fairly exotic and unavailable in a fiber form. Until very recently, silica fibers had not produced cooling because of the high concentration quenching of all trivalent rare-earth ions in this silica-based glasses. Quenching not only generates undesirable internal heat that overwhelms ASF cooling, but it also limits the maximum achievable Yb concentration, and therefore the heat that can be extracted.

    After nearly two decades of research, breakthrough work finally overcame this obstacle at the end of 2019, with two independent reports of cooling in silica. This presentation will describe the principle of ASF cooling, and its challenges specific to optical fibers. It will then go over the technological developments that have led to the production of high-purity silica fibers with compositions that tolerate record Yb concentrations and not only exhibit cooling but do so at atmospheric pressure. This work was rewarded with the recent demonstration of the first cooled fiber amplifier, a device that exhibits 17 dB of gain while the entire 4.5-m fiber remains slightly below room temperature. The talk will end with the latest development in this exciting new field—the first cool fiber laser, also made with a silica fiber. This solution to a long-standing fundamental limitation opens the door to a new class of fiber lasers and amplifiers with unprecedented coherence, stability, and low noise.

    Speaker Bio(s): 

    Michel Digonnet is a professor in the Applied Physics Department at Stanford University, California, where he received his MS and PhD in photonics. His current research interests focus on achieving record-breaking sensitivity in a wide range of fiber sensors, including gyroscopes, hydrophones, accelerometers, and strain sensors, utilizing in particular slow light and exceptional points. He is also working on rare-earth-doped fiber lasers and amplifiers for particle acceleration and laser refrigeration. He has published around 350 articles and issued over 150 patents. He is the co-inventor of the fiber optic amplifier, a cornerstone and now ubiquitous component that enabled the deployment of the high-speed Internet in the late 1990s. He has edited several books, chaired numerous conferences on fiber devices and optical materials, and taught graduate classes and courses on lasers, fiber amplifiers, and sensing.


    Colloquium will start at 3:30pm, following will be a meet and greet.